With recent development of communication techniques, various techniques for transmitting packets efficiently have been provided (for example, refer to Patent Reference 1). As one of these, a Moving Picture Experts Group Transport Stream (MPEG-TS) signal defined in the IEC 61883-4 has been conventionally transmitted by connecting a digital broadcasting tuner with a DVHS system video recorder in a room in a general home, using an IEEE 1394 method digital interface. Here, in the case where broadcast contents have been subjected to content protection such as Copy One Generation, the contents are encrypted and transmitted in order to protect the contents from unauthorized copying. As an example of a scheme for encrypting AV data such as an MPEG-TS obtained by receiving and selecting digital broadcast in this way and transmitting the AV data, the Digital Transmission Content Protection (DTCP) is defined. DTCP is a content protection technique used on a transmission medium such as the IEEE 1394 and a USB. The DTCP method has defined by Digital Transmission Licencing Administrator (DTLA), and described in the following: hyperlink “http://www.dtcp.com” “http://www.dtcp.com”; hyperlink “http://www.dtcp.com/data/dtcp#tut.pdf” “http://www.dtcp.com/data/dtcp#tut.pdf”; hyperlink “http://www.dtcp.com/data/wp#spec.pdf” “http://www.dtcp.com/data/wp#spec.pdf”; and book “IEEE 1394, AV Kiki e no Ouyo (Appkication to IEEE 1394, and apparatuses)”, edited by Shinji Takada, THE NIKKAN KOGYO SHIMBUN, LTD., Chapter 8, Copy Protection, pp. 133 to 149.
An MPEG-TS will be described. A transport stream is composed of transport packets (TS packets). A TS packet is a fixed-length packet of 188 bytes. The length is determined considering consistency with an ATM cell length and applicability in the case of performing error correction coding of a Reed-Solomon code or the like. A TS packet is composed of packet header having a fixed length of 4 bytes, and an adaptation field and a payload each having a variable length. In the packet header, a packet identifier (PID) and various types of flags are defined. According to this PID, the type of TS packet is identified. There may exist both adaptation_field and payload or only one of them. The presence can be identified by a flag (adaptation_field_control) in the packet header. An Adaptation_field has a function of transmitting information such as Program_Clock_Reference (PCR) and a function of stuffing within a TS packet in order to generate a TS packet with a fixed length of 188 bytes. Also, PCR is a timestamp of 27 MHz. The value of the PCR is referred to in order to reproduce a reference time at the time of coding in the System Time Clock (STC) of a decoding apparatus. In a TS of MPEG-2, the STC of the decoding apparatus has a PLL synchronous function by the PCR. In order to stabilize this PLL synchronous function, the transmission interval of the PCR is 0.1 ms at most. An MPEG-PES packet in which individual video streams, audio streams and the like are segmented into payloads of TS packets each of which has an identical PID number, and the TS packets are transmitted. In addition, such PES packet is configured to start with a starting position of a TS packet. Since a transport stream can transmit plural programs, table information is used. The table information indicates relationship between each program included in the stream and the program components such as video and audio streams which constitute the program. This table information is called Program Specific Information (PSI), and a Program Association Table (PAT) and a Program Map Table (PMT) are used. PSI such as a PAT and a PMT are positioned in the payload of a TS packet on a so-called section basis, and transmitted. The PIDs of PMTs corresponding to program numbers are specified in the PAT, and video, audio and additional data included in the corresponding program and the PIDs of the PCRs are described in the PMT. Therefore, with reference to the PAT and PMT, it is possible to extract only the TS packet which constitutes a desired program from among the streams. As a Reference Document concerning TS, there is, for example, “Gazo & Onsei Asshuku Gijutsu no Subete (Intanetto/dejitaru terebi, mobairu tsushin jidai no hissu gijutsu) (The Everything of Video and Audio Compression Technology (The Essential Technology in the Internet/a Digital Television and Mobile Communication Era)”, CQ Publishing, TECH I, Vol. 4, edited by Hiroshi Fujiwara, Chapter 6, “Gazo ya Onsei wo Tajuka suru MPEG Shisutemu (The MPEG System of Multiplexing Video and Audio)”, and the book explains TS.
As for logical hierarchical structures concerning a PSI and an SI, a processing procedure example, and a station-selection processing example, they are explained in “Dejital Hoso jushinki ni okeru Senkyoku Gijutsu (A Channel Selection Techniqhe by a Digital Broadcast Receiver)”, Miyake et. al., SANYO TECHNICAL REVIEW, Vol. 36, June, 2004, No. 74, pp. 31 to 44.
In addition, as for an access control scheme used in digital broadcasting, the ARIB standard and the ARIB STD-B25 define scrambling, specifications of related information and specifications of receivers concerning them. ARIB technical documents, the ARIB TR-B14, and the ARIB TR-B15 define the operation.
FIG. 1A is an example of transmission in the IEEE 1394 of an MPEG-TS using the DTCP method. In the DTCP method, the transmitter side (packet transmitter apparatus) is called source 1801, and the receiver side (packet receiver apparatus) is called sink 1802. Encrypted contents such as an MPEG-TS are transmitted from a source 1801 to a sink 1802 through a network 1803. As supplemental information, an example of a source apparatus and a sink apparatus will also be described in FIG. 1B.
FIG. 2 is a diagram illustrating the outline of a conventional packet communication unit in the DTCP method. Here, both of the packet transmitter unit provided with the source 1801 and the packet receiver unit provided with the sink 1802 in FIG. 1 are shown as packet transmitter and receiver units. First, authentication and key exchange (abbreviated as AKE) according to the DTCP method are performed. In an AKE unit 1901, the setting information of the authentication and key exchange is inputted. This information is transmitted to a packet generation unit 1902. The packet generation unit 1902 generates packets each having a prescribed header, and the packets are outputted to a network 1907. Here, the packet generation unit 1902 generates packets of inputted data using transmitting parameters determined by a transmitting condition setting unit 1903, and transmits the packets. In the receiver side, a packet receiver unit 1904 filters signals to be inputted through the network 1907 by identifying packet headers, and the obtained signals are inputted in the AKE unit 1901. In this way, the AKE unit of the transmitter side (source) and the AKE unit of the receiver side (sink) can perform message communication with each other through the networks 1803 and 1907. In other words, according to the DTCP method, authentication and key exchange are executed.
Once the authentication and key exchange are established between the transmitter side (source) and the receiver side (sink), AV data is transmitted next. In the source, an MPEG-TS signal is inputted into an encryption unit 1905, and encrypts the MPEG-TS signal. Subsequently, this encrypted MPEG-TS signal is inputted into the packet generation unit 1902, and outputted to the network 1907. In the sink, the packet receiver unit 1904 filters signals to be inputted through the network 1907 by identifying packets based on packet headers, and the obtained signals are inputted into the decryption unit 1906, and the decrypted MPEG-TS signal are outputted.
Next, a supplemental description of the above procedure will be provided next with reference to FIG. 3. In FIG. 3, the source and the sink are connected through the IEEE 1394. First, a content transmission request is made in the source side. Subsequently, encrypted contents and content protection mode information are transmitted from the source to the sink. The sink analyzes the copy protection information of the contents, determines the authentication method among a full authentication and a restricted authentication, and transmits the authentication request to the source. The source and the sink share an authentication key according to the processing prescribed in the DTCP. Subsequently, the source encrypts an exchange key using the authentication key, and transmits the encrypted exchange key to the sink. The sink decrypts the exchange key. The source generates seed information which changes as time passes in order to change the encryption key temporally, and transmits it to the sink. The source generates an encryption key, based on the exchange key and the seed information. The source causes the encryption unit to encrypt the MPEG-TS using this encryption key and transmits it to the sink. The sink receives the seed information, and restores a decryption key, based on the exchange key and the seed information. The sink decrypts the encrypted MPEG-TS signal, based on this decryption key.
FIG. 4 is an example of an IEEE 1394 isochronous packet in the case of transmitting an MPEG-TS signal in FIG. 1. Each of these packets is composed of a header of 4 bytes (32 bits), a header CRC of 4 bytes (32 bits), a data field of 224 bytes, and a trailer of 4 bytes (32 bits). Among the CIP header and TS signal which constitute the data field of 224 bytes, only the TS signal is encrypted before being transmitted. Here, the information which is unique to the DTCP method is a 2-bit Encryption Mode Indicator (EMI) which is copy protection information and an Odd/Even (O/E) which is the LSB of the seed information. Since they exist in the header of the above 32 bits, they are transmitted without being encrypted.
However, in the above conventional technique, there are the following problems. The conventional DTCP method is intended for transmitting an MPEG-TS signal using isochronous packet in real time in the IEEE 1394. However, it has a big problem that it cannot transmit the MPEG-TS signal through the networks such as the Ethernet (registered trademark) (IEEE 802.3), the wireless LAN (IEEE 802.11), and other networks which are available for transmission of IP packets, using the Internet Protocol (IP) which is the standard protocol of the Internet.
In other words, it has a big problem that it cannot transmit contents subjected to digital copyright protection such as ground/BS digital broadcasting and server broadcasting between the packet transmitter apparatus and the packet receiver apparatus which are logically connected through IP, while protecting the copyright of the contents.
In addition, in the case of using the HyperText Transfer Protocol (HTTP) in live-broadcast transmission, a receiver side needs to calculate a header length to be added in the encryption and the transmission content length, each time an HTTP request is made. Therefore, it has a problem that the processing load in a receiver side is heavy.
Further, it has a problem that it has difficulty in performing trick playback of contents stored in a hard disc or the like in a simple manner. Such trick playback includes fast forwarding, rewinding and slow playback.
Further, it has a problem that it has difficulty in performing trick playback of contents which have different storage formats and are stored in a hard disc, an optical disc or the like using a common scheme in a simple manner. Such trick playback includes fast forwarding, rewinding and slow playback. As an example of local operations (at an apparatus body) not operations via a network, as to trick playback in an apparatus body of Blu-ray disc scheme, the following explains the EP_map data structure for trick playback: “Logical Specifications and Content Protection System of Bru-ray Disk Rewritable Format (2)” in the Matsushita Technical Journal, October, 2004, pp. 34 to 38.
In particular, in a home, a digital television or a home server or the like needs to distribute contents which are subjected to digital copyright protection and obtained through broadcasting or the like to various types of apparatuses which are set in the home. Accordingly, it is necessary in the home to distribute contents according to the DTCP method in a form of wide-spread IP packets in order to enable content transfer between apparatuses of various manufacturers, while protecting the copyrights of the contents. In other words, there is a need to realize the Digital Transmission Contents Protection over IP (DTCP-IP).
(Patent Reference 1) Japanese Laid-Open Patent Application No. 2000-59463.